The basic trace is updated to include 3-fills. In line marking, rows dominate with fewer unmarked cells.

On the line marked grid, the tight square of 5’s has the slink corner for a hidden unique rectangle, Type 1. If 3r5c7 is true, 5r5c7 is not, and two corners are 5, the other two, 3. Now 3 and 5 interchange for a second solution.

Nothing is found in the bv scan or the X-panels,

before Sudokuwiki ventures into coloring with this trap. Both green and blue remove 9r2c7. The resulting NEr1 boxline removes 9r1c5, expanding the cluster.

Entering AIC building, an AIC nice loop combines an XY-chain, a reversed bv, and two X chains, one grouped.

A grouped cluster expansion is accompanied by a long and winding AIC boomerang.

The removal enables a Type 2b uniqueness rectangle. If 9r1c2, the ur candidate opposite the slink is true, the other ur candidate 5r8c2 is true and 5r8c5 is false. The slink makes 5r9c5 true.

The 5/9 placements in the rectangle can be interchanged for a second solution copying this one everywhere else.

In the trap, 2r2c2 is rejected by both blue and green. And in the East, an XY boomer starts from r4c7.

Sudowiki piles on with a third AIC boomer, and after

an XY chain placing S5,

and after

the bv field looks ripe for another cluster.

The red orange cluster is extensive, but short lived. In r1, if red is true, both blue and green are false. Then in c7, if we accept orange, we have to take blue as well.

Next is the conclusion of the updated review of Emanuel Castillo’s Only Extreme Sudoku.

In case you want to try the last review puzzle OnEx 390 on your own, work with this copy, because recovering the givens from the original review would give you too much in advance.

]]>The ALS X-chain boomerang starts with the 9-chain emerging from r9c7 and terminating on the 9 candidate of ALS 249, which slinks to the 4 value group. The group sees 4 in the starting cell, via 4-chain.

Independent of that elimination is this grouped AIC ANL,

and this one, the third grouped AIC ANL of the series.

This time the elimination expands the cluster and enables an XY-chain.

A boomer that didn’t work before is activated by the new c8 slink.

Then an AIC ANL turns 7r7c3 green and traps 7r8c3.

The AIC building series finally ends with an ALS boomer placing 8r7c6.

The S8 clue brings a naked pair 29, enabling a swordfish, which removes 2r1c7 for a hidden pair 29.

The hidden pair removals trigger an XY chain that starts a major expansion of the cluster.

Or a merge if a second cluster had already been started. The r8c3 trap turns 8r8c2 green, trapping 8r9c2. The naked pair r9s13 confirms 4r9c5, confirming N4 and S2.

Trace-wise,

The wrap brings immediate collapse.

Next, the update of the Only Extreme review continues with OnEx 347.

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The only move prior to AIC Building is this Type 2 unique rectangle, which enables the limited cluster and intersecting XY chain extended in the original post into a decisive coloring network by six trials.

The placement 6r9c1 brings the NWc1 boxline removing 3r2c2.

Sudokuwiki AIC building starts with a possible boomerang that finds an ALS node to get to an AIC almost nice loop(ANL).

The starting links are recycled into a grouped AIC ANL.

The first boomer has an obscure start, but comes back in an XY-chain.

Moving right to left in the South tier, boomer 2 is double grouped. The key is the first group, making the following slink out of r9c2.

Now that first boomerang throw can be recycled, including the same ALS, for an AIC ANL.

The breaking point is the nice loop, which introduces Medusa coloring to supplement Sudokuwiki.

The cluster expands and north tier AIC boomer links with it.

The 7r2c8 removal provides the needed slink for a hidden unique rectangle, Type 2. If 4r1c7 is true, so is 7r6c7 and 4r6c8. The slink then makes 7r1c8 true, and the rectangle’s 4’s and 7’s interchange for a second solution, no matter what happens elsewhere.

It’s been a lot to wade through, but *Only Extreme* 304 requires a lot more. For next week, I’m sending you on a scavenger hunt. You are to collect, in this order, an ALS X-chain boomer(4r9c6), a grouped AIC ANL(4r7c6), another grouped AIC ANL(8r7c2), an XYchain(2r2c8), an X-chain extended XY boomer(2r9c7), an AIC ANL(7r7c6), a coloring trap(7r8c3), and an ALS AIC boomer (1r7c6), a swordfish(2r1c8), a hidden pair, an XY chain(2r2c1), and after a large cluster expansion, a wrap.

Short of the final advanced coloring, you could just load the starting grid into Sudokuwiki and tap your way through it. If you do that, look up unfamiliar terms in the Guide and compare Sysudoku explanations with Sudokuwiki notes and drawings over this post. The drawings and spotting notes will be in the scavenger awards post next week.

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With Sudoku experience – or the interest to work through the Basic Sudoku pages of the Guide – you can read the Basic traces of Sysudoku posts and observe its humanly efficient manner of solving basic level puzzles, while preparing the grid for advanced methods. It’s done by observing how your own solving steps are ordered and expressed in the trace.

Here is the folded trace for the last pre-selected puzzle of the *Classic Sudoku* review, Classic 240.

The review table for *Classic Sudoku* reveals a surprising range of difficulty level. Six of ten are Basic level. Four collapse in the bypass, while one is beyond advanced, requiring an AIC building project.

The book contains no notes about the collection, so we don’t know whether this diversity is intended or not. The cover description of “Very Hard” just doesn’t fit. Most collections are much more consistent on a level of difficulty.

Turning now to Only Extreme 261, here is the line marked grid, with a hidden unique rectangle, Type 2b that I missed in the post of 11/28/2017, Pattern Coloring Not-Both on Only Extreme 261. The UR is signaled by the naked pair and a slink from one of its corners. If 8r7c3 is placed, the rectangle corner placements can be interchanged for a second solution.

Since trials was an issue in the Only Extreme review, it is relevant that NEr1 is a single alternate Sue de Coq, whose alternate term 8(27+72) solves 261 outright. The case was not closed with this trial, because there was hope for examples of not-both trial coloring extensions.

In the original post, a 7-chain ANL and an irregular 562-wing hinged at r4c8 are the only eliminations ahead of AIC building. In a failing session of AIC building, the not-both extension of an AIC slink was seen to be equivalent to a color trial of a pattern based cluster found earlier on the 7-panel. With help from a pattern analysis trap on the 8-panel, the trial turned out to be easy and decisive. But this success left open whether or not OnEx 261 could be solved without a trial.

Putting the question to Sudokuwiki in this update, the solver catches the 7-chain ANL, and moves directly to AIC building, demonstrating this AIC confirming ANL,

followed by a relatively easy boomerang (left below),

and the duplication of the irregular XYZ effect by an AIC boomerang.

After the grouped ALS boomerang here, Sudokuwiki stalls, leaving only the limited blue/green cluster.

The 5-panel eliminations have left a single olive and three pink patterns.

Fortunately for trial avoidance, the three orphans include the blue 5r9c4, confirming green.

As the grid opens up, an irregular 152-wing brings more bv.

Sudokuwiki is revived by these results, and puts together an AIC double grouped confirming ANL.

After the follow up below, the red/orange cluster of the original post is overwhelming.

Red is wrapped in c8 and orange mops up.

Next is the update on Only Extreme 304 originally solved by six trials over two posts, starting 12/05/17. With help from the Sudokuwiki solver, it is solved without trial.

Puzzles requiring extensive AIC building are deserving of a difficulty level to themselves. Reserving the “extreme” level for those requiring trials, Sysudoku will be calling the new level the AIC-net level.

]]>First, the bypass trace of Classic 216:

Get out a grid, copy in the givens from the previous post, and account for every move. The 3-fills are signaled by square brackets. Its challenging and worth it.

Now for Only Extreme 132, the critical pattern analysis occurs on the 7-panel, where freeforms from r1 enumerate three patterns. Orange and red colors are assigned, because coloring the single pink freeform red and the candidates common to the two olive freeforms orange, we have a second coloring cluster. An immediate benefit is that three orphans are eliminated.

Back on the grid, the new red/orange cluster undergoes a very unusual wrap. The intersection of clusters in r1c4 shows that red implies blue. But in the south tier, a red 7 and Sudoku slink marking would confirm 6r7c8, implying not blue. Red cannot be true, therefore orange must be.

The resulting expansion of the blue/green cluster brings a productive XY chain, but the lesson here is how the remaining candidates of the two orange patterns form a third cluster, immediately wrapped for an immediate collapse. It’s all traced and displayed in the updated post.

Next up is the conclusion of the *Classic Sudoku* review, with Classic 240. Following that is an update of the post of 11/08/17 in which a Not-Both trial, with help from pattern analysis, reaches a solution of Castillo’s Only Extreme 261. In the update, the same pattern analysis rescues a Sudokuwiki impasse to solve 261 without trial.

First, a Basic trace of Classic 192. It can be solved in the bypass.

For the Advanced level resolution of Only Extreme 3, start with the Basic grid and trace posted on August 29, 2017.

This time, right out of the hidden pair line marked grid, Andrew Stuart’s Sudokuwiki found a BARN, a.k.a. Bent Almost Restricted *n*-Set. After the BARN, the i186-wing, 4-chain, finned 5-wing and Wr4 Sue de Coq, still apply.

Then on the 6-panel a grouped nice loop takes out three 6-candidates.

An 8-chain triggers a naked pair.

In AIC building, two reverse bv support a confirming ANL.

The follow up marking includes a hidden dublex.

Coloring may be overdue. The blue/green cluster expands with two traps, with follow up marking.

This leads to three more traps, with follow up marking

Blue is confirmed, and the solution is immediate.

Next is Basic level Classic 216 and a report on the update of Only Extreme 132, originally posted 10/24/17. The pattern analysis that rescues an indecisive not-both trial now solves OnEx 132 without trials.

]]>The Classic 168 box marked grid has four lines marked, and four free cells in four more lines.

The middle line in the trace below is the box marking. Below that is every move, in order, of the collapse of Classic 168 into a solution, on the second line, column 1 of line marking.

It may be difficult for casual readers to realize what the trace is. The Guide pages will open the trace, and systematic Sudoku, to anyone.

Now about the review of Manuel Castillo’s *Only Extreme Sudoku*. It’s the second collection review selected for update, after KrazyDad’s *Insane* collection. These updates are undertaken on the hardest puzzles, and are reworked with backup from the Sudokuwiki solver available to everyone on Andrew Stuart’s site.

The original post of 10/17/17 solved *Only Extreme* 89 by a *Single Alternate Sue de Coq*, a Sysudoku trial innovation. Then it was shown that a freeform pattern analysis on one X-panel put four patterns in the pink slice and only one in the olive slice, and that the key clue isolated by the SASdC belongs to the single pattern. Either trial solves OnEx 89

The update solves OnEx 89 without trial, by full use of AIC building, including the recently recognized boomerang type of ANL.

Gratifying but not significant for the solution was this BARN, or Bent Naked Almost Restricted 4-set. BARNs are one of the friendly interpretive disputes between Sysudoku and Andrew Stuart.

Sudokuwiki found it and I didn’t, but stretching the definition of the WXYZ-wing to cover it, as the solver notes do, is not helping anyone to spot it.

At the bottom here is the SASdC. It’s logic is explained in the updated post.

After an easy finned X-wing and a 12-link boomerang, this ALS node eliminating ANL and an ALS node confirming ANL, or boomerang if you prefer, bring a respectably logical collapse.

C’mon, you have to __look__.

Next in the Classic review is 192 at right, and an updated solution of Castillo’s Only Extreme 3 below, originally posted 8/29/2017, where it demonstrates trials to extend coloring clusters onto slinked AIC segments. The updated solution avoids trials.

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The boomer parade pauses for a pair of AIC ANL. This one uses reversed bv to switch from 2-chain to 8-chain and back again.

On the same base, the top is shifted for a second ANL.

Sudokuwiki adds one more boomer, a grouped one, that produces two naked pairs.

As the first cluster is added, Sudokuwiki finds a confirming AIC ANL.

The follow up marking

creates an ample field of bv for a second cluster.

The red/orange cluster is no sooner created, than wrapped by a newly created 798-wing. An orange 8r7c2 sees the toxic set, and the red candidates lead the collapse.

After all those boomerangs, an XYZ-wing? That’s Sudoku.

Next up in the review is Classic 168, shown here. The remaining four pre-selected review Lpuzzles are resolved in Basic. For that reason, basic traces of remaining Classic puzzles will be combined with reports on updated posts from Manuel Castillo’s *Only Extreme Sudoku*. Next week, the first update report is on Only Extreme 89, originally posted 10/17/2017.

Your first checkpoint is this grid as box marking ends. A built-up naked triple is left for the marking of four rows to follow.

Line marking is tough, even with the naked triple and a hidden pair removing four candidates in r5c1.

The first two Advanced moves are simple X-chain ANL. They’re superimposed on the line marked grid.

A Sudowiki follow up is this APE worthy of a Guide example. Restrictions on red cell pairings include a separated ALS in c8, taking out the 27 pairing, joining the 79 pairing to remove 7r3c8.

After this hidden single follow up,

a grouped 2-chain ANL rounds out the X-panel attack.

The removal supports another APE defining example, allowing a box ALS to participate.

Coloring doesn’t get started here, so its time for AIC building.

The KrazyDad Insane update showed that AIC hinges are not used frequently enough to mark ahead of AIC building. Cell winks of other kinds are too often useful to have the pre-drawn AIC hinges distract attention from them.

In Boomer 1 the 3-slink emerging from r1c7 is an XY-chain.

Boomerangs 2 and 3 start with the 8-chain out of r2c6, with XY transitions to 2 and then to 6. One returns to 6r2c6. The other, to XY to see 3.

The first AIC boomer is the fourth, with the 5-slink AIC using an AIC hinge and two reverse bv to go to 4, 5 and 9 into starting cell r7c1.

Boomer 5 emerges on 5 and XY-chains to 1 and 6, and 6-chains on back to the starting cell r1c6.

The same chain is used in a back up boomer 6, starting with a 4 from cell r1c4.

Going back one, boomer 5’s 6r1c6 removal adds a second slink for this hidden unique rectangle, Type 1. If 2r7c6 is true, the slinks force 6 in the two adjacent corners and 2 in the opposite corner, a composer’s nightmare.

Let’s pause for an opportunity for you to finish Classic 144 your way. There’s plenty of action left.

Next post, this report continues AIC building a few more eliminations, then builds and wraps two coloring clusters.

]]>With Classic 93, the bypass was over quickly and box marking completed the 9’s. Then three lines in, a hidden single starts a rapid collapse. Along the way, you see a chain of identical bv 38 develop and collapse before reaching remote pair length.

Here is the grid, just after the naked single and hidden single, and just as the collapse is starting. Following a collapse, like box marking and line marketing, is a routine activity. But it is also satisfying, like knitting and whittling. The trace looks complicated to the uninitiated. But it builds itself, with simple, efficient steps.

On Classic 120, we have only the bypass to report. The trace spreads across the page, before dropping in the collapse, leaving many causes unused.

For Advanced only readers, Forest’s Classic 144 is worth waiting for. It requires a parade of boomerangs, and has a surprising Sysudoku finish.

After that, the Classic review finishes in Basic, along with reports updating another review . If you have a needed update in mind, let me know in a comment.

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